The specific activity of natural 87Rb was measured by means of 4pibeta liquid scintillation counting in a two-photomultiplier-tube spectrometer. 3H-efficiency tracing was used together with the CIEMAT/NIST method to obtain the detection efficiency. For this purpose a new parameterization of the shape factor for the third forbidden non-unique beta-transition was performed. The hygroscopic behaviour of the salts used for sample preparation was studied. The half-life of 87Rb was found to be T1/2 = 4.967(32) x 10(10)y.